JPH0747111B2 - Method and apparatus for separating organic liquid mixture - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for separating or concentrating an organic liquid mixture by a pervaporation method using a specific polymer membrane.

[Prior Art] A process for separating an organic liquid mixture using a polymer membrane has been disclosed in US Pat. No. 2953502 and the like. For this separation process, a separation method generally called a pervaporation method is used, which supplies the liquid to be treated to the high pressure side (primary side) of the polymer membrane,
This is a method of preferentially permeating a substance that easily permeates to the low pressure side (secondary side) as vapor. This method is a liquid mixture that cannot be separated by a conventional simple method, for example, an azeotropic mixture,
It has attracted attention as an effective and energy-saving method for separating or concentrating a mixture system having a small relative volatility with boiling points close to each other and a mixture containing a substance which causes polymerization or transformation by heating.

In this pervaporation method, it is considered that permeation is promoted by lowering the pressure of permeated vapor on the membrane surface on the secondary side. At this stage, the secondary side is kept at a reduced pressure by a vacuum pump experimentally. Alternatively, an inert gas is passed as a carrier gas on the surface of the secondary side membrane to realize membrane permeation. As an industrial process, as disclosed in Japanese Patent Application Laid-Open No. 58-95523, a method of keeping the secondary side at a reduced pressure is being studied in many cases. Since the degree of pressure reduction on the secondary side greatly affects the separation performance of the membrane, it is preferable to keep the pressure on the secondary side as low as possible in order to fully exert the membrane performance and perform efficient concentration and separation. . In laboratory-level tests, there are many cases where tests are usually performed at several mmHg or less.

Further, when the purpose is to concentrate and separate the organic liquid component from the aqueous solution, the permeated vapor must be collected. In this case, it is introduced into a cold trap under a reduced pressure or an inert gas stream to be condensed. In order to increase the collection efficiency and reduce the loss amount, it is necessary to sufficiently cool the trap, and it is necessary to lower the cooling temperature of the cold trap as the degree of vacuum on the permeate side is increased.

[Problems to be Solved by the Invention] However, the pervaporation method is at a test and research level for industrialization at this stage, and in terms of industrial technology, an ordinary vacuum pump holds a large-capacity device at a high degree of vacuum. There was a problem that it was difficult to do.

Further, as an industrial technique, the process of keeping the trap at a low temperature has a problem that it consumes the most energy. Therefore, it is necessary to raise the cooling temperature of this cold trap as high as possible and to sufficiently improve the collection efficiency. Is required.

The present invention provides a technique for efficiently combining a vacuum pump and a mechanical booster pump to reduce the burden on a cold trap or to omit it, and to efficiently separate a target object in a high vacuum.

[Means for Solving Problems] In order to achieve the above object, the present invention has the following configuration.

(1) In a method of separating an organic liquid mixture by a pervaporation method, a mechanical booster pump is provided between a membrane module and a vacuum pump, the compression ratio of the mechanical booster pump is set to 5 times or more, and a secondary side of the membrane module is provided. A method for separating an organic liquid mixture, characterized in that the degree of vacuum of the is maintained at 30 mmHg or less.

(2) An apparatus for separating an organic liquid mixture by a pervaporation method, wherein a mechanical booster pump is provided between a membrane module and a vacuum pump.

FIG. 1 shows a flow chart of a method for separating an organic liquid mixture and an apparatus according to the present invention, which will be specifically described. In the figure, 1 is a liquid supply layer of an organic liquid mixture, 2 is its circulation pump, 3 is a heating device, 4 is a pervaporation method membrane module, 5 is a mechanical booster pump, 6 is a cold trap, and 7
Indicates a vacuum pump. The organic liquid mixture to be treated is stored in the feed liquid layer 1 and the temperature of the feed liquid is adjusted to a predetermined temperature by the heating device 3 by the circulation pump 2 and then fed to the pervaporation membrane module. The circuit of the rear 8 is returned to the original liquid supply layer, and the organic liquid mixture is circulated. The secondary side of the membrane module is 30 mmHg or less, preferably
A vacuum level of 10 mHg or less is maintained, and a mechanical booster pump of 5 has a compression ratio of 10 mmHg or more, preferably 30 mmHg or more.
The permeated vapor is guided to the cold trap 6 by increasing the pressure more than twice, and the permeated vapor is condensed and collected, and then the degree of vacuum is maintained by the vacuum pump 7. The circuit 9 shown by the dotted line is for starting the operation of the secondary side by first evacuating the secondary side of the membrane module to a predetermined vacuum degree by the vacuum pump 7 and then starting the mechanical booster pump 5 through the circuit 9 It is a thing. The method of closing the circuit of the mechanical booster pump and operating only the vacuum pump of 7 by the circuit of 9 corresponds to the method which has been experimentally implemented in the past.

As the organic liquid mixture, it is possible to apply to all the organic liquid mixtures that are usually the target of the pervaporation method. That is, any liquid mixture containing at least an organic liquid as one of its constituents can be applied.

Specific examples of the organic liquid mixture include water-methanol, water-ethanol and water-propyl alcohol. Water-isopropyl alcohol, water-allyl alcohol, water-methyl ethyl ketone, water-acetone, water-ethyl acetate, water-butyl alcohol, water-amyl alcohol, water-furfuryl alcohol, water-tetrahitofuran, water-dioxane, water A representative example is a mixture of acetonitrile and the like. Also, methyl acetate-methanol, ethyl acetate-ethanol, benzene-cyclohexane, methanol-acetone, benzene-methanol, benzene-ethanol, acetone-fluoroform, methanol-
Acetone, ethylbenzene-styrene, parachloroethylbenzene, -parachlorostyrene, toluene-methylcyclohexane, butadiene-butenes, butadiene-
A mixture containing butanes as a main component is also included. However, it is not limited to these specific examples.

The temperature at which the organic liquid mixture is supplied to the membrane module is
The temperature can be adjusted to a predetermined temperature by a heating device placed in front of the membrane module, but it can also be adjusted by a feed liquid layer. In many cases, the upper limit is 80 ° C to 100 ° C due to the characteristics of the separation membrane. However, in the case of a membrane module using an inorganic porous membrane, the range of 100 ° C. or higher and the boiling point of the organic liquid mixture or lower is also possible.

The membrane module is not limited as long as it is a membrane module of the pervaporation method.

That is, the membrane material may be a natural polymer membrane, a membrane having a structure obtained by chemically modifying or modifying a natural polymer, a synthetic polymer membrane, or a separation membrane using an inorganic porous membrane. It may be a membrane or a membrane in which a separation active material is impregnated in a porous membrane.

When an aqueous solution is used, there are a membrane that selectively permeates water and a membrane that selectively permeates an organic liquid component, but any type of membrane may be used.

The membrane shape may be a hollow fiber membrane, a flat membrane, or a tubular membrane.

The basic type of the membrane module is a hollow fiber membrane module described in JP-B-39-28695, a hollow fiber membrane module described in JP-B-47-11696, and a spiral wound flat membrane described in JP-B-49-8629. It may be either a module or a so-called plate-and-frame type membrane module.

Basically, a normal roots pump is preferably used as the mechanical booster pump, but other types of dry pumps that do not use a sealing liquid may be used as long as there is no problem in corrosion resistance due to the properties of the organic liquid mixture. I don't care.

The degree of vacuum on the secondary side of the membrane module is adjusted to 30 mmHg or less, preferably in the range of 0.1 to 10 mmHg by selecting the exhaust capacity in consideration of the permeation amount, the mixed gas amount, and the leak gas amount. The degree of vacuum is preferably adjusted by adjusting the rotation speed of the mechanical booster pump with a pressure gauge on the secondary side of the membrane module, but it can also be performed by operating the leak valve in front of the mechanical booster pump with a pressure gauge. .

Vacuum level at the mechanical booster pump outlet, that is,
The vacuum degree at the inlet of the cold trap is calculated from the vacuum degree and the compression rate on the air supply side of the booster pump in consideration of the collection rate (or loss rate) of the cold trap, and hence the relationship between the vapor pressure of the permeated component and the cooling temperature. It is determined. The degree of vacuum is adjusted by selecting the exhaust capacity of the vacuum pump with respect to the exhaust volume of the booster pump and operating the leak valve in front of the vacuum pump with a pressure gauge on the exhaust side of the mechanical booster pump. Usually 10 mm
It is determined in the range of Hg or more, preferably 30 mmHg or more and 100 mmHg or less. For example, as a preferable condition, the booster pump has a compression ratio of 5 times or more, but if the compression ratio is 10 times and the degree of vacuum on the secondary side of the membrane module is 5 mmHg,
The degree of vacuum on the exhaust side of the mechanical booster pump can be set to 50 mmHg. Therefore, the cooling of the cold trap can be reduced, and at the same time, the load on the vacuum pump can be reduced.

In the present invention, it may be unnecessary to collect the permeated vapor component with the cold trap. An example of such a case is a case where water is taken out from an organic liquid. Particularly in a system in which water is dehydrated from water-containing ethanol, only water can be taken out as a permeated vapor and the whole amount can be removed by evacuation with a vacuum pump. In such a case, the pump capacity can be set so that the power consumption becomes most advantageous.

The cold trap can be cooled with dry ice cryogen or liquid nitrogen in the case of a small-scale device, but at the industrial level, it is preferable to use a cooler capable of arbitrarily adjusting the cooling temperature. preferable. The trap type may be a coil type or a multi-pipe type, but it is necessary to prevent the passage of the pipe from being blocked due to icing. It is preferable that a plurality of traps are of a switching type and provided with a leak circuit and a preliminary vacuum circuit so that they can be continuously operated.

As the vacuum pump, an ordinary oil rotary pump, a multi-blade rotary pump, a water-sealed pump, a dry vacuum pump or the like can be used in one stage, or a pump of the same type or a blade type can be used in combination in multiple stages.

[Embodiment] A specific description will be given according to the flowchart shown in FIG.

Membrane for pervaporation is supplied at a rate of 3l / min using a glass sealless centrifugal pump 2 by supplying 10wt% aqueous solution of ethinol to 40l thermostat 1 with temperature control and adjusting to about 60 ° C. Cycle to module 4. Heating device 3
Is a system in which a stainless steel coil is connected to the front side of the membrane module and the device immersed in a water tank is set to 60 ° C. The temperature of the aqueous ethanol solution supplied to the membrane module is 60 ° C ± 1 ° C
Adjusted to. For the membrane module of 4, a plate-and-frame type membrane module having an effective membrane area of 10 cm × 10 cm was used. The separation membrane is made of poly [1
-(Trimethylsilyl) -1-propyne] film
Ten sheets were used to form a membrane module with a total effective area of 0.1 m ² . As the mechanical booster pump 5, a roots pump with a displacement of 108 m ³ / hour with an electric motor of 0.4 kw / hour was used. The above-mentioned poly [1- (trimethylsilyl) -1-propyne] is a film material known from JP-A-60-75306.

The vacuum pump 7 has a displacement of 330 l / 0.75 kw / hour with an electric motor.
A minute oil rotary pump was used, connected after the cold trap 6. The degree of vacuum on the secondary side of the membrane module was adjusted by operating a leak valve with a vacuum gauge. The degree of vacuum at the mechanical booster pump outlet side, that is, the cold trap inlet was also adjusted by a leak valve provided between the cold trap and the oil rotary vacuum pump. As the cold trap, a coil type trap having a capacity of 4 liters, which can control the cooling temperature in the range of -20 ° C to -100 ° C, was used at -50 ° C.

After closing the circuit of the mechanical booster pump and the pressure on the secondary side of the module, that is, the inlet side of the mechanical booster pump has reached 10 mmHg, operate the mechanical booster pump and close the circuit 9 to break in for about 2 hours. Did. After the break-in operation, the cold trap was switched and the operation state was measured for 4 hours and recorded during that time, and the permeated vapor was collected to measure the ethanol concentration. The ethanol concentration was measured by gas chromatography. As a result, the degree of vacuum on the secondary side of the membrane module and the pressure on the outlet side of the mechanical booster pump could be easily maintained at 1.5 mmHg and 30 mmHg, respectively. The oil rotary vacuum pump has a displacement of 60 ml / min or less and 0.2 kw.
/ It has been found that a vacuum pump with an electric motor for about an hour is sufficient. It was The amount of the aqueous ethanol solution trapped is
The concentration was 61.5% at 472 g.

(Comparative Example) The comparative example was operated according to the example, but the mechanical booster pump was not operated, and the comparative test was performed only with the oil rotary vacuum pump having a displacement of 330 l / min. As a result, it was found that the ultimate vacuum degree on the secondary side of the membrane module was 1.7 mmHg, and a vacuum pump with a larger displacement was necessary to achieve a vacuum degree of 1.5 mmHg or less. The aqueous methanol solution collected in the cold trap was 346 g in 4 hours and the ethanol concentration was 49.7% as in the example. The difference between the collected amount of ethanol and the example was about 120 g, and it was found that cooling to −75 ° C. or lower was necessary to obtain a collection rate equivalent to that of the example.

[Advantages of the Invention] (1) The mechanical pump and the rotary vacuum pump can adjust the degree of vacuum at the cold trap inlet, and the energy required for cooling can be reduced.

(2) By combining a mechanical booster pump and a rotary pump, the secondary side of the pervaporation membrane module can be maintained at a desired degree of vacuum with a smaller amount of power consumption, and membrane performance is improved. You can

[Brief description of drawings]

FIG. 1 is a flow chart showing the configuration of the present invention. 1 is a supply liquid layer, 2 is a supply liquid circulating through the membrane module
Supplying pump, 3 heating temperature device, 4 pervaporation membrane module, 5 mechanical booster pump, 6 cold trap, 7 vacuum pump, 8 supply liquid return circuit, 9 bypass for mechanical booster pump The circuit is shown.

Claims (6)

[Claims] 1. A method for separating an organic liquid mixture by a pervaporation method, in which a mechanical booster pump is provided between a membrane module and a vacuum pump, and a compression ratio of the mechanical booster pump is set to 5 times or more. A method for separating an organic liquid mixture, characterized in that the degree of vacuum on the secondary side is maintained at 30 mmHg or less. 2. The method for separating an organic liquid mixture according to claim 1, wherein the organic liquid mixture is a water-containing liquid containing an organic liquid substance as a main component. 3. The method for separating an organic liquid mixture according to claim (2), wherein the organic liquid substance is soluble in water and has a lower boiling point than water. 4. A method for separating an organic liquid according to claim 1, wherein a cold trap is provided between the mechanical booster pump and the vacuum pump. 5. An apparatus for separating an organic liquid mixture by a pervaporation method, wherein a mechanical booster pump is provided between a membrane module and a vacuum pump. 6. An organic liquid separating apparatus according to claim 1, wherein a cold trap is provided between the mechanical booster pump and the vacuum pump.